optical transmission equipment according to the present invention time-division multiplexes a plurality of relatively low-speed optical signals from a tributary side using a TDM MUX to a signal with a specific wavelength λ1, wavelength-multiplexes it together with other relatively high-speed wavelengths λ2 . . . λn from the tributary side using a WDM MUX, and outputs the multiplexed signal λ1∼λn to an aggregate side. The equipment also receives the optical signals λ1∼λn from the aggregate side, performs an operation reverse to the one described above, and outputs demultiplexed signals to the tributary side.
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4. A method of optical transmission comprising the steps of:
multiplexing a plurality of optical signals having multiple wavelengths and demultiplexing said multiplexed optical signals, wherein said multiplexing step comprises the steps of: converting a portion of said optical signals having multiple wavelengths to electrical signals; time-division multiplexing said converted electrical signals to a first high-speed electrical signal; converting said first high speed electrical signal into a first high speed optical signal via an electrical/optical conversion unit; and wavelength multiplexing a remaining portion of said optical signals having multiple wavelengths, and said first high-speed optical signal; and wherein said demultiplexing step comprises the steps of: wavelength-demultiplexing a wavelength-multiplexed optical signal into a plurality of wavelength demultiplexed optical signals, said first high-speed optical signal being one of said plurality of wavelength-demultiplexed signals; converting said first high speed optical signal into said first high speed electrical signal; time-division demultiplexing said first high-speed electrical signal to a plurality of electrical signals; converting said plurality of electrical signals to optical signals each having different wavelengths; and converting a remaining portion of said plurality of wavelength demultiplexed optical signals into optical signals each having different wavelengths. 1. optical transmission equipment, comprising:
a multiplexing unit that multiplexes a plurality of optical signals having multiple wavelengths and; a demultiplexing unit that demultiplexes a multiplexed optical signal; wherein said multiplexing unit comprises: an optical multiplexing conversion unit having a plurality of optical/electrical conversion units which convert a portion of said plurality of optical signals to a plurality of electrical signals; a time-division multiplexing unit which time-division multiplexes said plurality of electrical signals from said optical/electrical conversion units to a first high-speed electrical signal; an electrical/optical conversion unit which converts said first high speed electrical signal to a first high speed optical signal, said optical transmission equipment further comprises: a wavelength multiplexing unit which wavelengths-multiplexes optical signals including a remaining portion of said plurality of optical signals with a plurality of different wavelengths, and said first high-speed optical signal; and wherein said demultiplexing unit comprises: a wavelength demultiplexing unit which wavelength demultiplexes a wavelength-multiplexed optical signal to a plurality of optical signals with a plurality of different wavelengths, said plurality of optical signals including said first high speed optical signal and a remaining portion of wavelength demultiplexed optical signals; at least one optical/electrical conversion unit which converts said first high-speed optical signal to said high-speed electrical signal; a time-division demultiplexing unit which demultiplexes said first high-speed electrical signal to a plurality of electrical signals; a plurality of electrical/optical conversion units which convert said plurality of electrical signals to optical signals having different wavelengths; and a plurality of optical/electrical/optical conversion units which convert said remaining portion of wavelength demultiplexed optical signals to a plurality of optical signals each having different wavelengths. 2. optical transmission equipment according to
3. optical transmission equipment according to
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This invention relates to an optical network element (hereafter called an O-NE), which is optical transmission equipment for use in an all-optical network using multiplexing/demultiplexing routing based on optical wave length, and to an optical transmission method.
Recently, as the amount of data traffic has increased rapidly, a need has arisen for a higher, larger-capacity transmission network. Conventionally, a network element (hereafter called an NE) for use on a transmission network has used Time Division Multiplexing (hereafter called TDM). To process a large volume of transmission data, an NE using Wavelength Division Multiplexing (WDM) has become popular on a network. The introduction of WDM has led an O-NE to employ not only optical wavelength multiplexing but also optical wavelength switching and routing.
In this specification, the swung dash (∼) is used to indicate wavelength-multiplexed signals, and the ellipses (. . . ) to indicate signals not wavelength-multiplxed.
In addition to the WDM, there are other O-NEs: an Optical Add-Drop Multiplexer (hereafter called OADM) and an Optical Cross-Connect (hereafter called OXC).
The optical wavelength used for WDM is defined by ITU-T as about 1550 nm. The number of multiplexed wavelengths using this wavelength is approximately 40 or so, with the maximum being 80-100. For optical path routing in the all-optical network, one wavelength is assigned to transmission from one end customer to another end customer. Therefore, the number of wavelengths is a bottleneck of building a large network. Especially, in a backbone network where a large number of optical signals are received from access networks, the limit on the number of wavelengths is a serious problem.
Earlier patent disclosures relating to the present invention are found in Japanese Patent Application No. Hei 2-162939 (U.S. Pat. Nos. 5,144,466 and 5,343,314) and in Japanese Patent Application No. Hei 7-30771. However, the problem described above is not described in these patent applications. The optical cross-connect and optical ADM technology are described in "Integrated Lightwave Networks" (FUJITSU 48, 5, 436-411).
In view of the foregoing, it is an object of the present invention to provide optical transmission equipment, that is an O-NE, and optical transmission method which solve the problems involved in building a large optical network and which help to build an efficient and economical all-optical network.
In the all-optical network, optical signals from the nodes of end customers are routed at an optical wavelength level to form a network. An optical signal itself has various bit rates. In SDH/SONET networks, low-speed systems use 50 Mb/s, 150 Mb/s, and 600 Mb/s, and high-speed systems use 2.4 Gb/s and 10 Gb/s. In non-SDH/SONET networks, low-speed units use 45 Mb/s, 100 Mb/s, and 200 Mb/s and high-speed units use 1 Gb/s. The bit rate of many optical signals from end customer nodes in access networks, for example, from those in SDH/SONET networks, is 2.4 G/s or lower. The bit rate of most signals is 600 Mb/s or lower.
When these optical signals are transmitted over an optical network, many optical wavelengths are necessary because each optical signal requires its own optical wavelength. This makes it difficult to build the network. In addition, in a case of allocating a low bit rate to an optical wavelength, it is not economical in terms of transmission capacity because the optical wavelength originally capable of transmitting a high-speed signal is used for a low-speed signal.
In view of the foregoing, the O-NE according to the present invention multiplexes a plurality of relatively low-speed optical signals in the TDM mode to convert them to a high-speed electrical signal. A new type O-NE is provided according to the present invention, which has a function of converting the electrical signal to an optical signal with another optical wavelength in order to solve the above-described problem. The O-NE according to the present invention is called Optical Gateway Equipment.
Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which:
An embodiment of the present invention will be described below with a network complying with the SONET (Synchronous Optical Network) standard as an example.
First, referring to
Referring to
The number of optical signals (λ11 . . . λ1i, λ21 . . . λ2j, λ31 . . . λ3k) from the tributary side is determined by the multiplexing rule of SONET. For example, when there are only 150 Mb/s signals (OC-3), the number of optical signals is 64 (i=64, j=0, k=0); when there are only 600 Mb/s signals (OC-12), the number of optical signals is 16 (i=0, j=16, k=0); when there are only 2.4 Gb/s signals (OC-48), the number of optical signals is 4 (i=0, j=0, k=4). When the signals of 150 Mb/s (OC-3), 600 Mb/s (OC-12), and 2.4 Gb/s (OC-48) are mixed; for example, when there are 16 (sixteen) 150 Mb/s (OC-3) signals, 4 (four) 600 Mb/s (OC-12) signals, and 2 (two) 2.4 Gb/s (OC-48) signals, that is, i=16, j=4, and k=2. In such a way, relatively low bit-rate optical signals are thus aggregated into a high-speed optical signal λ1.
The relatively high bit-rate 2.4 Gb/s optical signals (OC-48) λ41 . . . λ4a from the tributary side are converted to 2.4 Gb/s (OC-48) optical signals λ2 . . . λc by an optical/electrical/optical conversion unit (hereafter called O/E/O) 10. The 10 Gb/s (OC-192) optical signals λ51 . . . λ5b are converted to 10 Gb/s (OC-192) optical signals λd . . . λn by an optical/electrical/optical conversion unit (hereafter called O/E/O) 12.
As described above, the optical signals from the tributary side are aggregated and converted to optical signals λ1 . . . λn, multiplexed by the WDM MUX 9 into one optical signal λ1∼λn, and sent to the aggregate side.
Referring to
In this embodiment, (i+j+k) relatively low-speed optical signals are converted to electrical signals, time-division multiplexed, and then converted to a high-speed optical signal with one wavelength. Conversely, a high-speed optical signal with one wavelength is converted to an electrical signal and time-division demultiplexed, and converted into (i+j+k) relatively low-speed optical signals. This alleviates the limit of the number of wavelengths, and enables provision of transmission equipment capable of highly efficient transmission.
Another embodiment of the optical gateway equipment according to the present invention will be described with reference to
The present embodiment differs from the embodiment described above in the function to convert relatively low-speed signals to high-speed optical signals through TDM. That is, because the total bandwidth of low-speed optical signals is large, a function in which the low-speed optical signals are aggregated into a plurality of high-seed optical signals is added in the present invention. In this embodiment, the 150 Mb/s, 600 Mb/s, and 2.4 Gb/s electrical signals are time-division multiplexed to 10 Gb/s electrical signals by the TDM MUX 7, and are converted to a plurality of 10 Gb/s (OC-192) optical signals λ1 . . . λc by the E/O 8. Conversely, one optical signal λ1∼λn is demultiplexed to the optical signals λ1 . . . λn by the WDM DMUX 22. The 10 Gb/s (OC-192) optical signals λ1 . . . λc are converted to 10 Gb/s electrical signals by the O/E 21 and are time division demultiplexed to 150 Mb/s, 600 Mb/s, and 2.4 Gb/s electrical signals by the TDM DMUX 20.
In the present embodiment, (i+j+k) relatively low-speed optical signals are converted to electrical signals, time-division multiplexed, and then converted to a plurality of high-speed optical signals each with its own wavelength. Conversely, a plurality of high-speed optical signals each with its own wavelength are converted to electrical signals and time-division demultiplexed, and converted into (i+j+k) relatively low-speed optical signals. This alleviates the limit of the number of wavelengths, providing transmission equipment capable of highly efficient transmission. Compared with the embodiment described above, the present embodiment is advantageous when there are many relatively low-speed optical signals.
A further embodiment according to the present invention will be described with reference to FIG. 13. A cross-connect type optical gateway equipment will be described in this embodiment. On the aggregate side, there are m input optical signals and m output optical signals, each composed of n multiplexed optical signals with wavelengths λ1∼λn. On the tributary side, there are input and output demultiplexed optical signals, each composed of optical signals λ11 . . . λ3k and optical signals λ41 . . . λ5b. When adding signals on the tributary side, the optical multiplexing conversion unit 27 described in the above embodiment aggregates the optical signals λ11 . . . λ3k into the optical signal λ1 and converts the optical signals λ41 . . . λ5b to optical signals λ2 . . . λn. They are input to an optical space division switch 29. These optical signals λ1 . . . λn are switched by the optical space division switch 29, wavelength-multiplexed by the WDM MUX 9, added to the optical signals λ1∼λn, and output to the aggregate sides 1 . . . m. As shown in the figure, if the output port m+1 is selected by the optical space division switch 29, the optical signals may be dropped onto the tributary side instead of being added to the aggregate side.
The optical signals λ1∼λn from the aggregate sides 1 . . . m are demultiplexed by the WDM DMUX 22 to optical signals λ1 . . . λn and are input to the optical space division switch 29. These optical signals λ1 . . . λn are switched by the optical space division switch 29. The signals to be dropped onto the tributary side are converted to optical signal λ11 . . . λ3k (generated by demultiplexing the optical signal λ1) and optical signals λ41 . . . λ5b by the optical demultiplexing conversion unit 28 described in the above embodiment. As shown in the figure, when the optical space division switch 29 selects the corresponding output port, the optical signals λ1∼λn from the aggregate side may be passed to any of m aggregate sides in the wavelength unit as its optical signals λ1∼λn.
In the above-described embodiment, the optical multiplexing conversion unit 27 and the optical demultiplexing conversion unit 28 described in
In this embodiment, (i+j+k) relatively low-speed optical signals are converted to electrical signals, time-division multiplexed, and then converted to high-speed optical signals with one or more wavelengths. Conversely, high-speed optical signals with one or more wavelengths are converted to electrical signals and time-division demultiplexed, and converted into (i+j+k) relatively low-speed optical signals. This alleviates the limit of the number of wavelengths, so that an optical cross-connect type optical gateway equipment capable of highly efficient transmission can be obtained.
Another embodiment according to the present invention will be described with reference to FIG. 14. An OADM optical gateway equipment is used in the present embodiment. On the aggregate side, there are two input optical signals and two output optical signals, each composed of n multiplexed optical signals with wavelengths λ1∼λn: one for the West side and the other for the East side. On the tributary side, there are input and output demultiplexed optical signals, each composed of optical signals λ11 . . . λ3k and optical signals λ41 . . . λ5b. When adding signals on the tributary side, the optical multiplexing conversion unit 27 described above aggregates the optical signal λ11 . . . λ3k into the optical signal λ1 and converts the optical signals λ41 . . . λ5b to optical signals λ2 . . . λn. They are input to the optical space division switch 29. These optical signals λ1 . . . λn are switched by the optical space division switch 29, wavelength-multiplexed by the WDM MUX 9, added to the optical signals λ1∼λn, and output to the East aggregate side 1 and the West aggregate side 2. As shown in the figure, if the corresponding output port is selected in the optical space division switch 29, the optical signals may be dropped onto the tributary side instead of being added to the aggregate side.
The optical signals λ1∼λn from the West aggregate side 1 and the East aggregate side 2 are demultiplexed by the WDM DMUX 22 to optical signals λ1 . . . λn and are input to the optical space division switch 29. These optical signals λ1 . . . λn are switched by the optical space division switch 29. The signals dropped onto the tributary side are converted to optical signals λ11 . . . λ3k (generated by demultiplexing the optical signal λ1) and optical signals λ41 . . . λ5b. As shown in the figure, when the optical space division switch 29 selects the corresponding output port, the optical signals λ1∼λn from the West aggregate side 1 and East aggregate side 2 may be passed to the East aggregate side 1 and the West aggregate side 2 as the optical signals λ1∼λn by the wavelength base.
In the above-described embodiment, the optical multiplexing conversion unit 27 and the optical demultiplexing conversion unit 28 described in
In this embodiment, (i+j+k) relatively low-speed optical signals are converted to electrical signals, time-division multiplexed, and then converted to high-speed optical signals with one or more wavelengths. Conversely, high-speed optical signals with one or more wavelengths are converted to electrical signals and time-division demultiplexed, and converted into (i+j+k) relatively low-speed optical signals. This alleviates the limit of the number of wavelengths, providing an OADM type optical gateway equipment capable of highly efficient transmission.
The optical gateway equipment 100-2 on the other end transmits the demultiplexed 150 Mb/s optical signal λ11 . . . λ1i, 600 Mb/s optical signals λ21 . . . λ2j, and 2.4 Gb/s optical signals λ31 . . . λ3k to an OADM ring in the access network not shown in the figure.
The two units of gateway equipment connected in the point-to-point mode may be gateway equipment 100'.
Next, the optical path routing method using the optical gateway equipment used in the present embodiment will be described.
As shown in
Therefore, as shown in
As described above, the present invention provides an optical network element (O-NE) and optical transmission equipment that may be used in a large optical network in which wavelength based multiplexing and routing are performed.
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